Furnace



Nov. 21, 1939. E. H. BERRYMAN FURNACE Filed Feb. 13, 1937 3 Sheets-Sheet l F'Ill- FURNACEl 3 Sheets-Sheet 2` l N V EN TOR. f//mf'f effymw 1wA 45?: z TTORNEY E. H. BERRYMAN Filed Feb. 13, 1957 Nov. 2l, 1939.

Nov. 2l, 1939. E. H. BERRYMAN 2,180,577

FURNACE Filed Feb. 13, 1937 3 Sheets-Sheet 3 INVENTOR. f/f/Ver H errymaf? ATTORNEY.

Patented Nov. 21, 1939 UNITED STATES PATENT OFFICE 7 Claims.

This invention relates to dental casting furnaces and is an improvement to the furnace disclosed in the Berryman Patent No. 2,017,337 of October 15, 1935.

In operating furnaces such as disclosed in my prior patent above referred to, some difficulty has been found in renewing or replacing the heating elements. In making castings under superatmospheric pressure, it has been found that in some instances the gasket disposed between the work supporting member, in which the investment ring is accommodated, and the lower face of the furnace is injured when the work supporting means is moved away from the furnace proper, due to the residual air pressure existing within the furnace. Furthermore, it has been found that when large investment rings are used such as shown in Figure 6 of my Patent No. 2,017,337 which cannot be entirely housed within the furnace, it is difiicult to maintain the investment ring up to temperature. Consequently there is a tendency for the investment to cool and shrink, making the mold smaller and causing the casting to be smaller than required.

One of the objects of this invention is the proyision of a pneumatically operated dental casting furnace in which the heating element or elements may be readily changed or replaced.

Another object of the invention is the provision of a pneumatically operated dental casting furnace having means whereby the interior of the furnace may be vented to atmosphere before the furnace is opened, in order to prevent injury to the gaskets.

A further object of the invention is the provision, in combination with a dental casting furnace, of a heater for surrounding the exposed surfaces of an investment ring when the investment ring is operatively associated with the furnace.

The invention possesses other advantageous features, some of which with the foregoing will be set forth at length in the following description where that form of the invention which has been selected for illustration in the drawings accompanying and forming a part of the present specification is outlined in full. In said drawings, one form of the invention is shown, but it is to be understood that it is not limited to such form, since the invention as set forth in the claims may be embodied in a plurality of forms.

Referring to the drawings:

Figure l is a vertical section taken on the broken line I-I of Figure 4 with parts broken -away ring a sight opening 6.

showing a dental casting furnace embodying the objects of my invention.

Figure 2 is a section taken on the line 2-2 of Figure 1.

Figure 3 is a section taken on the line 3--3 v5 of Figure 1.

Figure 4 is a section taken on the line 4--4 of Figure 1.

Figure 5 is a section taken on the line 5 5 of Figure 1.

Figure 6 is a partial vertical section of a dental casting furnace in combination with a heating element surrounding a large investment ring when the investment ring is operatively asso- ,y ciated with the furnace. '15

As shown in various gures of the drawings, my invention may be embodied in a dental casting furnace comprising a rectangular casing I provided on its lower face with a boss 2 through which a circular opening 3 is formed. The upper 520 face of the casing I is provided with a threaded nipple 4 adapted to receive a cap 5 and contain- Secured over the upper end of the nipple 4 by means of the cap 5 is a sight glass 1. In order to make an air tight .25 joint between vthese members, gaskets 8 may be used as shown in Figures 1 and 5. One end of the casing I is provided with a flange 9 to which is detachably secured by any suitable means such as screws a cover plate I I. In order to hermeti- '.30 cally seal the cover plate II to the flange 9, a gasket I2 may be interposed between these two members.

Snugly accommodated within the casing I and inserted therein through the flanged end of the 35 casing is a rectangular block I3 of any suitable refractory material. The block I3 is provided with a central sight opening I4 in registration with the sight opening 6 of the nipple 4, and the lower face of the block is provided with a recess "40 I5. It will be noted that the lower portion of the recess I5 is rectangular in form while its upper portion or ceiling is upwardly concave. Disposed within the recess I5 is a cradle or tray I6 formed on its upper face with a pair of :45 parallel spaced longitudinally extending semicircular recesses I1 and I 8. The tray I5 is also provided with a central vertical circular opening I9 in line with the sight opening I4 of the refractory block I3. Seated within the recesses `50 I1 and I8 formed in the tray I6 are resistance elements 2| and 22, the extremities of which are of enlarged diameter as shown in Figures 4 and 5. By so constructing these resistance elements,

`theirendsare snugly accommodated within their .55

respective recesses and the electrical resistance at their ends is relatively low with respect to their central portions. The rear ends of the resistance elements 2i and 22 are connected by means of a metal clip 23. The forward end of the resistance element 2l is secured by means of a metal clip 24 to a binding post 25 and the forward end of the resistance element 22 is secured by means of a clip 26 to a binding post ZI. The binding postsv 25 and 2'I are secured to and extendlthrough the lower Wall of the casing I, as best shown in Figure l. It will be noted that the clips 24 and 25 are apertured at their endsr so as to tightly nt over the tapered upper ends of the binding posts 25 and 2.

The casing I is supported by and secured to the legs 23 by means of screws 29, and the legs 28 are provided intermediate their ends with threaded lugs BI to which is secured by means of screws 32 a shelf 33. The shelf 33 is formed with a central bore 32 adapted to receive ascrew 35 and with a counter-bore 36 adapted to rotatably receive thehnange 3l formed onthe upper end of an interiorly threaded sleeve 38. The ange 3l is held in the counter-bore'33 by a plate 39 riveted to the shelf 33. Secured to the sleeve 38 by a pin 4I is a hand wheel 42. 'Ihe screw 35 is formed with a longitudinally extending slot t3 adapted to receive a pin IQ secured to the shelf From this construction it will be noted that the pin lid engaged within the slot 43 prevents the rotation of the screw 35 and that therefore the rotation of the hand wheel 42 will cause the screw 35 to travel in a vertical direction.

The upper end of the screw 35 is accommodated in a socket li5 formed in the lower end of a work supporting member ii and is secured thereto by means of a pin fl'I. The upper face of the work supporting member 46 is recessed to accommodate an annular gasket 48 and is formed with a counter bore d@ for accommodating an investment ring 5l. The investment ring 5l is provided with an interrupted thread v52 adapted to be received in a complementary interrupted thread 53 formed in the bore IIS. The interrupted threads 52 and 53 form in eiect a bayonet and slot connection and serve to quickly attach and detach the investment ring to and from the work supporting member. In order to form a hermetical seal between the investment ring and the work support 46, an annular gasket member 54 is interposed between these two members. The floor of the work supporting member it is formed with a central recess 55 and communication between this recess and atmosphere is established by means of a passageway 55.

As shown in Figure 4, an air line 5'I is secured to the casing l and establishes communication with 'the interior thereof and a suitablesource of super-atmospheric pressure through a twoway valve 58.

To operate the device as above described, the investment ring 5I is secured to the work supporting member 4.3. The gold button 53 is placed in the depression in the investment material and the work supporting member is screwed and sealed against the boss 2 of the casing I, all as shown in Figure l. The binding posts V25 and 21 are then connected to a source of electric current and the interior of the furnace brought to a temperature sufficient to melt the gold button 59. The condition of the gold button may be observed through the sight glass 1, and when it is in a molten state, the valve 58 is so adjusted as to permit air under super-atmospheric pressure to pass into the casing I and force the molten gold into the mold formed in the investment material. The air confined within the mold is thereby forced into the central recess 55 and passes to atmosphere through the passageway 55. After the molten gold has passed into the mold formed in the investment material and it is thought that a Well-defined inlay has been formed, the valve 58 is adjusted so as to establish communication between the atmosphere and the casing I, thereby equalizing the pressures on either side of the casing I. When this has been done, the work supporting member 46 may be 1 lowered by rotating the screw 42 and the investment ring 5I removed by a pair of tongs and quenched in the usual manner.

The ring 5I and the investment material contained therein expand with an increase in temperature. The investment material is so chosen as to its coeflicient of expansion that when the inlay molded in it cools to room temperature, the inlay will exactly correspond to the size of the cavity for which it was mad-e. In order to maintain the ring and its contents to temperature, it is desirable as shown in Figure 1 that the openings 3 and I9 be sufliciently large to leave a space about the ring 5I for the free circulation of hot air.

In some instances it is desired to use an investment ring of such dimensions that it cannot be accommodated within the circular opening 3 formed in the bottom of the casing I. An investment ring 6I of this character has been shown in Figure 6 as provided with an upwardly extending conical neck 62. The lower end of the investment ring EI is supported by the work supporting member 46 and is sealed thereto by means of the gasket 48, while its upper end is sealed against the boss 2 of the casing I by means of the gasket 48'. It will be noted that although the conical neck 62 of the investment ring 6I extends through the opening 3 of the casing I, the peripheral surface of the body of the investment ring falls entirely outside of the opening. In order to maintain the body of the investment ring to temperature, so that the gold within the investment material will not cool and shrink, a cylindrical heating element 33 is made to sturound the body of the investment ring. The cylindrical heating element S3 may be made of i either a refractory material or insulating material and has embedded in its inner surface a resistance wire 54 adapted to pass through a handle 65 and thereby be connected to any suity able source of electric current. It will be noted that by this arrangement my casting furnace may be effectively used in connection with investment rings of such size that they cannot pass through the opening in the bottom of the furnace, and by the use of a cylindrical heating element surrounding the investment ring, the temperature of the investment ring may be maintained at any desired degree. The operation of the furnace as shown in Figure 6 is identical with the operation of the furnace as shown in Figure 1 with the exception that the cylindrical heater B3 must of course be disposed over the investment ring before the investment ring is secured between the bottom of the casing I and the work supporting member 5.16.

I claim:

1. A casting furnace comprising: a casing having an opening in the bottom face thereof; a block of refractory material accommodated in said casing and provided with a recess in registration with the opening in said casing; a tray of refractory material disposed in said recess and provided with a central opening in line with the opening in said casing; a resistance element supported on said tray; means for connecting said resistance element to a source of electric current; and means for holding an investment ring in registration with the opening in the bottom of said casing.

2. A casting furnace comprising: a casing having an opening in the bottom face thereof and a detachable end wall; a block of refractory material accommodated in said casing and provided with a recess in its lower face in registration with the opening in the bottom face of the casing; a tray of refractory material disposed in said recess and provided with a vertical opening in line with the opening in the bottom of the casing; a resistance element supported on said tray in line with the vertical opening therein; means for connecting said resistance element to a source of electric current; and work supporting means adapted to be held against the lower face of said casing in registration with the opening therein.

3. A casting furnace comprising: a casing having an opening in its bottom face and a detachable cover for one side thereof; a block of refractory material accommodated in said casing and provided with a recess in its lower face in registration with the opening in the bottom face of the casing; a tray of refractory material disposed in said recess and provided with a vertical opening in line with the opening in the bottom of the casing; a recessed seat formed in the upper face of said tray; a resistance element disposed in said recessed seat in line with the vertical opening in said tray; means for connecting said resistance element to a source of electric current; and work supporting means adapted to be held against the lower face of said casing in registration with the opening therein.

4. A casting furnace comprising: a casing having an opening in its bottom face and a detachable cover for one side thereof; a block of refractory material accommodated in said casing and provided with a recess in its lower face in registration with the opening in the bottom face of the casing; a tray of refractory material disposed in said recess and provided with a vertical opening in line with the opening in the bottom of the casing; a plurality of spaced recessed seats formed in the upper face of the tray; resistance elements disposed in said seats in line with the vertical opening in the tray; means for connecting said resistance elements to a source of electric current; and work supporting means adapted to be held against the lower face of said casing in registration with the opening therein.

5. A casting furnace comprising: a casing having an opening in its bottom face and a detachable cover for one side thereof; a block of refractory material accommodated in said casing and provided with a recess in its lower face in registration with the opening in the bottom face of the casing; a tray of refractory material disposed in said recess and provided with a vertical opening in line with the opening in the bottom of the casing; a pair of spaced, parallel, longitudinally extending recessed seats formed in the upper face of said tray; resistance elements disposed in said seats in line with the vertical opening in the tray; means for connecting said resistance elements to a source of electric current; and Work supporting means adapted to be held against the lower face of said casing in registration with the opening therein.

6. A casting furnace comprising: a casing having a circular opening in its bottom face; a block of refractory material accommodated in said casing and provided with a recess in its lower face in registration with the opening in the bottom face of the casing; a tray of refractory material disposed in said recess and provided with a vertical opening in line with the opening in the bottom of the casing; an opening formed in one of the lateral faces of said casing and through which said block and said tray may be passed; a detachable cover secured over said last mentioned opening; a resistance element supported on said tray in line with the vertical opening therein; means for connecting said resistance element with a source of electric current; and work supporting means adapted to be held against the lower face of said casing in registration with the circular opening therein,

7. A casting furnace comprising: a casing having a circular opening in its bottom face; a block of refractory material accommodated in said casing and provided with a recess in its lower face in registration with the opening in the bottom face of the casing; a tray of refractory material disposed in said recess and provided with a vertical opening in line with the opening in the bottom of the casing; an opening formed in one of the lateral faces of said casing and through which said block and said tray may be passed; a detachable cover secured over said last mentioned opening: a resistance element supported on said tray in line with the vertical opening therein; means for connecting said resistance element with a source of electric current; a cylindrical investment ring of greater diameter than the diameter of the circular opening in the bottom face of said casing; means for holding said investment ring against the bottom face of said casing and in line with the circular opening therein; and a heating element surrounding said investment ring.

ELMER I-I. BERRYMAN. 

